Most of small-scaled speaker systems have an enclosure of closed box type or bass-reflex type. A prior art base-reflex type speaker system is shown in FIGS. 1 through 4 where an enclosure comprises a case 1 and a front baffle 2. The front baffle 2 supports a woofer SP.sub.1 and a tweeter SP.sub.2, and has a port from which a duct cylinder 3 defining a duct extends into the interior of the enclosure 1. Reference numeral 4 denotes a protector made of rubber or other equivalent material to protect a rear glass member. Since the enclosure is small-scaled to meet an expected limited amount space, the duct cylinder 3 also has a limited dimension. Therefore, the prior art speaker system involves the following problems. Namely, due to the limited dimension of the enclosure, it is not prevented that some intermediate frequency waves radiated rearward from the woofer SP.sub.1 come out of the interior to the exterior of the enclosure through the duct 3. These waves join the intermediate frequency waves radiated directly frontward by the woofer SP.sub.1 and deteriorate the sound quality. Further, the limited dimension of the duct 3 unables a decrease of synchronous frequencies and a sufficient reproduction in low frequencies.